Permeability-tuned resonant circuit



Oct. 30, 1934. w. .1. POLYDOROFF PERMEABILITY TUNED RESONANT CIRCUIT Filed July 8, 1935 A INVENTOR #Z/w/M/EfPaL vac/ear BY M 6 AITORNEY Patented Oct. 30, 1934 UNITED STATES rsaarsaBmrrr-rrmsn nEsoNaNr CIRCUIT Wladimir J. Polydoroif, Chicago, Ill., assignor to Johnson Laboratories, Inc., Chicago, 111., a cornotation of Illinois Application July 8, 1933, Serial No. 079,474

' 6 Claims. (01'. 250-40 The present invention relates broadly to resonant circuits, and more particularly to those cases wherein it is necessary or desirable to provide a plurality of adjustments. In cases where l several resonant circuits are used, for example in a cascade arrangement, or in cases where particularly refined tuning adjustments are tobe made, it is usual to employ several adjustments to establish the initial electrical and mechanical 10 conditions in the system. The novel arrangements and'devices herein disclosed are especially advantageous in systems in which the tuning operation is accomplished by the insertion into the coil which formsa part of the resonant circuit,

of a magnetic core body, such, for example, as is described in my co-pending application No. 523,112 on Magnetic core materials. The invention herein disclosed may, however, have utility in systems tuned by other methods of inductance variation, or in systems tuned bycapacity variation. It may also be useful in systems wherein no means is provided for tuning over any 'considerable band of frequencies, but in which adjustments are nevertheless desired to tune the circuit or system to a particular single frequency.

In my co-pending application No. 667,368, for Improvements in inductive tuning systems", which is addressed more particularly to systems in which a plurality of resonant circuits is used,

I have shown that it is desirable to have not less than three adjustments in each of the resonant circuits of the system, or in at least all but one of the circuits. These adjustments are additional to the tuning means itself, by which the plural magnetic bodies are moved in unison with respect to the coils, to tune the system, as a whole, to any desired frequency within its range of adjustability. The three adjustments are preferably employed at three different frequencies, one at either end of the range and one near the center of the range, to produce very close agreement in resonant frequency between the several circuits at these particular frequencies, and substantial agreement throughout the range. The electrical nature and behavior of these adjustments, and

a preferred mechanical arrangement embochring them, are adequately set forth in the co-pending application referred to. i

. so 'In the manufacture of those classes of appaare assembled with the other parts. The final adjustments are ordinarily made, therefore, after the apparatus has been assembled, and after all necessary wiring has been installed. In the mechanical design of such apparatus, it is frequently a matter of considerable difilculty to so arrange the numerous parts that access can still be had to the means for adjusting the resonant circuits. Moreover, the assembled apparatus frequently has considerable weight and bulk. Inconvenience and unnecessary increase in production ,cost result if the adjustments are difficult to reach, or if the complete apparatus must be turned around, or turned over, in order to gain access to them.

It is obviously desirable, therefore, that all the adjustments for the plural resonant circuits which must be finally set after assembly should be located on one side or face of the apparatus, or so that they can be easily reached from one side. The side'or face chosen will depend on the design of the apparatus, and the method and arrangements employed in the assembly and test, but the tuning unit, or the unit which includes the plural resonant circuits, will be so placed as to give the maximum convenience in adjustment.

In systems tuned by inductance variation produced by relatively movable magnetic cores, there are two adjustments on each resonant circuit, in addition to adjustment means on the cores themselves. The core adjustments are ordinarily made before the cores are assembled onto the apparatus, but the remaining two adjustments are preferably made after assembly. One of these adjustments is to establish the capacity in each circuit at the proper value, and the other is to establish each coil in its proper position relative to its cooperating core. 1

The principal object of the present invention is to provide mechanical means for these two final adjustments, which will satisfy the conditions outlined above in a simple and reliable manner. As will be set forth in detail, in connection with the description of the drawing, the adjustments for each one of the several tuned circuits are conveniently brought outat one side of the tuning unit or circuit assembly, and may be easily and accurately set at the desired position by the use of suitable tools. Further objects of the invention, and advantages resulting from its use, will be apparent from what follows.

Referring now to the drawing, which is illustrative of a preferred embodiment of the invention, and in which the numerals refer to the same parts in all views:

Fig. 1 is an elevation, partly in section, of a complete tunable resonant circuit, except that no means for moving the magnetic core relatively to the coil are shown;

Fig. 2 is aview of the lower or left hand end 01' Fig. 1, except that a difl'erent form of mounting plate is shown; I

Fig. 3 is an enlarged partial section corresponding to a portion of Fig.1;

Fig. 4 is a diagrammatic representation of circuits similar to that of Fig. 1, arranged in a tuning unit; and

Fig. 5 is a wiring diagram showing how such a system of resonant circuits may be efiectively connected for use.

The resonant circuit illustrated in Fig. 1 consists of a coil structure, 1, and a condenser, 2. The circuit is tuned over a desired band of frequencies by varying the eifective permeability oi the space surrounding the coil. This is accomplished by the magnetic core, 3, which is arranged, by any suitable mechanical means, to be moved relatively to the coil structure, 1. As will be seen, the core, in this case, has been designed with an annular recess or cavity, 311, to receive the coil, the relative motion of the core and coil being parallel with their common axis. With the core in the position, relative to the coil, shown in Fig. 1, the core has a negligible efiect upon the effective value of the inductance of the coil, and the inductance inthe resonant circuit is therefore at a minimum value. As the core and coil are telescoped, the core increases the eflective permeability of the space surrounding the coil, and the effective value of the inductance in the resonant circuit is increased. When the coil has advanced into the recess as far as it will go, the

.maximum value of effective permeability is attained, and the efiective inductance in the tuned circuit is at a maximum.

The coil structure, 1, consists of a moulded form, 4, preferably slightly tapered toward its open or free end, and carrying a coil, 5, preferably of Litz wire, and having a single layer, wound in a thread moulded into .the form. The form, 4, is closed at the fixed end and carries a stem, 6, threaded at its outer end, the stem, 6, being moulded into the form, 4, as an insert.

The coil structure, 1, is adjustably mounted upon a base, '7, which is preferably of a highgrade ceramic insulation material- Through the base, 7,passes a sleeve, 8, threaded at one end, and having a head, 9, at its other end, of hexagonal or other suitable non-circular section. The base, 7, has an hexagonal recess, which receives a nut, 10, which, in turn, secures the sleeve, 8, to the base, '1. The stem, 6, of the coil, 1, passes through a hole in the sleeve, 8, and the hexagonal head, 9, engages a hexagonal recess in the base of the moulded coil form, 4. Between the end of the coil form, 4, and the base, 7, there is a compression spring, 11, which tends to push the coil, 1, away from the base, 7. At the outer end of the stem, 6, there is a nut, 12, by which the coil 'may be axially adjusted to any desired position with respect to the base, within the limits set by the engagement of coil form, 4, and hexagonal head, 9, and against the action of the spring, 11. The sleeve, 8, which is secured to the base, 7, by the nut, 10, prevents rotation of the coil, 1.

On the outer side of the base, 'I, is mounted a condenser, 2, of the usual semi-adjustable type, consisting of plates, 13, 14, separated by mica or other suitable dielectric members, 15. There are two plates, 13, 13a, which form one side of the condenser, the plate, 14, which forms the other side, being mounted between the two plates, 13, 13a, and being insulated from them by mica members, 15. The outer plate, 13, is preferably heavier than either of the plates, 13a, 14, is made 01' spring metal, and is slightly bent, so that normally only its edges bear on the mica.

Each of the plates, 13, 13a and 14, and the mica members, 15, has a large hole at its center, of such size as to adequately space them from the sleeve, 8. On the end or this sleeve there is a nut,

16, separated from the outer plate, 13, by an insulating washer, 17. By adjusting this nut 'on the sleeve, 8, the bent outer plate, 13, may be deformed so as to bring more or less of its surface into con-- tact with the mica member, 15. This increases or decreases the capacity of the condenser, 2, and permits accurate tuning of the resonant circuit to a particular desired frequency;

The plates, 13, 13a and 14, of the condenser, 2, have ears, 18, 19, which project through holes in the base, '7. These ears are provided with small holes at their ends, and serve as terminals to which the ends of the winding, 5, may be soldered, as shown, to form the resonant circuit. Connections from the resonant circuit to other parts or devices, not shown, may be conveniently soldered to these same terminals. The ears, 18, 19, also serve to center the condenser assembly on the base, 7, and to prevent it from turning.

All the metal parts, 6, 8, 10, 11, 12, 13, 14 and 16, are preferably made of a non-ferrous metal such as brass, in order not to afiect the inductance of the coil, 1 and in order not to increase its electrical losses excessively. The outer plate, 13, is of spring metal, such as spring brass, or phosphor bronze.

Fromthe above description, it will be seen that the two nuts, 12 and 16, which are bothaccessible on the outer end of the resonant circuit assembly, accomplish the two necessary adjustments,

namely, an adjustment of the capacity of the.

action of a spring member (11 and 13) and that therefore both adjustments are of such a nature that they will not change due to shocks or vibration.

, The base, '1, which carries the complete resonant circuit, may be mounted on any suitable supporting member, 21. This support, which may be the chassis pan of a radio receiver, or which may be a. separate member intended to support the several bases for the plural tuned circuits in a tuning unit, may have holes, 22, large enough to admit the base, 7, with small inwardly-projecting ears, 23, which are received in the recesses, 20, of the base, 7. An alternative method of mounting the base, '7, on the supporting plate, 21, is to use small spacing blocks, notshown, at the recesses, 20, to raise the base oil the support enough to give clearance to the condenser plate, 13, and insulatwhere several such circuits are to be used in the same apparatus, and it is desired to mount them as close together as possible. Such a shield, 24, is shown in Fig. 1, and consists of a non-ferrous metallic cylinder, surrounding and co-axial with the coil structure, 1, and the core, 3, and extending slightly beyond the end of the coil. This is of suflicient size to admit the core, 3, and is mounted directly on the member, 21, which supports the coil. Alternatively, the shield may be of square section, with rounded edges, and may have a lip at the outer end with a circular opening to admit the core.

The mechanism for moving the several cores in unison is fully described, in several different forms, in my co-pending application last above referred to. In general, it consists of a gang plate, 29, upon which the cores are mounted, guide means to permit only a, linear reciprocating motion of the gang plate with the cores, and suitable driving means to produce such motion, from a suitable knob or handle.

It will be apparent that many modifications of the arrangement described and shown in the drawing are possible without departing from the scope of the invention. For example, the sleeve, 8, might bemoulded into the base, 7, as an insert, and the nut, 10, dispensed with. Similarly, the condenser plates, 13, 13a, and 14, may have various configurations and arrangements of terminals, to adapt the resonant circuit to particular requirements. These and many other variations in the design will suggest themselves to those skilled in the art, to meet special conditions, without sacrificing the advantages of the arrangement of the two adjustments.

In the wiring diagram, Fig. 5, which is schematic, and shows only those elements and connections necessary for the purposes of the present specification, I have indicated a preferred method of connecting resonant circuits of the type herein described. It will be noted that the outer end of the coil is shown as being connected to actual ground,-25, or to an equivalent high-frequency ground, as at 26. The inner end of the coil is,

connected to the plate, 27, or to thegrid, 28, of the associated vacuum tube, as the case may be.

The two plates, 13, 13a, of the condenser, 2, are normally also connected to the ground, 25, or to the equivalent high-frequency ground, 26, and these terminals are therefore shown connected to the outer end of the coil. The internal plate, 14, of the condenser is preferably connected to the inner end of the coil.

In this method of connection, the free or outer end of the coil, into which the core first enters, is at low high-frequency potential, and therefore at substantially the same potential as the core, which, preferably, is also connected to ground. This materially decreases the capacity losses over what they would be if the opposite method of connection were used. When the core is about to enter the coil, the circuit is tuned to the higher frequencies of the range. It is therefore particularly important to keep the losses at this point as low as possible, because they tend to be at a maximum at the higher frequencies.

The method of connecting the condenser, 2, has the advantage that the internal plate, 14, which isconnected to the plate, 2'7, or grid, 28, of a vacuum tube, is at least partially shielded by the outer plates, 13, 13a, which are at low high-frequency potential.

Having thus described my invention, what I claim is:

1. A resonant circuit including an inductance coil, a condenser, and a relatively-movable magnetic core for tuning said circuit over a band of frequencies, said coil and said condenser being mounted on opposite sides of a base, and means external to the condenser and coaxial with the condenser and the coil whereby the capacity value of the condenser and the position of the coil relatively to the core may be initially established.

2. A resonant circuit including an inductance coil, a condenser, a magnetic core, means for rel: ative motion between said coil and said core for tuning said circuit over a band of frequencies and additional means external to the condenser and coaxial with the coil whereby the effective capacity and the :fiective inductance of said circuit may be adjusted for any position resulting from said relative motion.

3. A resonant circuit including an inductance coil and a condenser, a relatively movable magnetic core for tuning said circuit over a band of frequencies, and means external to the condenser and coaxial with the coil whereby the effective capacity and the effective inductance of said circuit may be independently adjusted.

4. A resonant circuit including an inductance coil, a condenser, and a relatively-movable magnetic core, said coil and said condenser being mounted upon opposite sides of a base and hav ing their terminals connected to form said resonant circuit, the end of said coil adjacent said base being so connected as to be at high highfrequency potential.

5. A resonant circuit including an inductance coil, a condenser, and a relatively-movable magto the condenser and coaxial with the coil for adjusting the capacity of the condenser and the position of the coil relative to the base.

WLADIMIR J. POLYDOROF'F. 

